Method for forming a reduced active area in a phase change memory structure

ABSTRACT

A phase change memory structure and method for forming the same, the method including providing a substrate comprising a conductive area; forming a spacer having a partially exposed sidewall region at an upper portion of the spacer defining a phase change memory element contact area; and, wherein the spacer bottom portion partially overlaps the conductive area. Both these two methods can reduce active area of a phase change memory element, therefore, reducing a required phase changing electrical current.

This is a Divisional of a application Ser. No. 10/791,607, filed on Mar.1, 2004 now U.S. Pat. No. 7,858,980.

FIELD OF THE INVENTION

This invention generally relates to microelectronic integrated circuit(IC) semiconductor device fabrication and more particularly to a methodfor forming a reduced active area of a phase change memory element toreduce a required phase changing electrical current.

BACKGROUND OF THE INVENTION

Phase change memory devices use phase changing materials, for example,materials where a phase change can be induced by an electrical energy,where a sufficient thermal heat induced by this electrical energy willresult in a temperature change in the phase change materials, forexample a current or voltage applied to the material to induce heatingin the phase changing material. For example, the phase changing materialmay change between amorphous and crystalline including partiallyamorphous and partially crystalline, the nature of the phased statebeing detectable, for example by a number of order in resistance change,typically is larger than one order, and thereby forming storedinformation. Typical phase changing materials suitable for memoryelements include those utilizing various chalcogenide elements, forexample one or more elements from Column VI of the periodic table. Oneparticularly suitable group of alloys is the GeSbTe alloys system.

Phase changing memory elements have several advantages over other typesof memory including DRAM, SRAM, and Flash memory. For example, they arenon-volatile and may be written to with high speed, e.g., less thanabout 50 nanoseconds. Since transistors are not necessary to accomplishthe read and write operations, the memory cells may be formed at highdensity. In addition, such memory cells are compatible with CMOS logicand are low power and low cost.

One goal for producing phase changing memory cells is to reduce thepower consumption by reducing the amount of drive current required toeffect a phase change in the phase changing memory element. The requireddrive current is dictated by the resistance of the phase changingmaterial as well as the active area of the phase changing material,which is dictated by the area to which electric contact is made to thephase changing material (phase change memory element) to deliver a phasechanging current. In general, assuming a given resistance of the phasechanging material, a smaller contact area produces a higher resistanceand therefore a higher level of resistive heating (temperature) for agiven applied writing (drive) current. Therefore a smaller electrodecontact area to the phase changing material memory element willcorrespondingly and desirably reduce drive current and thereby powerconsumption.

There have been various approaches in the prior art to reduce the phasechange memory cell electrode contact area (active area). In general,prior art approaches have relied on photolithographic and etchingtechniques to pattern and form as small a contact area as possible.These approaches are difficult to scale down in size due the limitedprocessing windows in lithographic and etching processes at the desiredsizes. Other approaches have relied on forming complicated memory cellstructures that rely on complicated and therefore costly processingsteps to produce various memory elements and electrode shapes.

Thus, there is a need in the semiconductor manufacturing art for animproved phase change memory element and method for forming the same toreduce an electrical contact area to the memory element thereby reducingpower consumption.

It is therefore an object of the invention to provide an improved phasechange memory element and method for forming the same to reduce anelectrical contact area to the memory element thereby reducing powerconsumption, while overcoming other shortcomings and deficiencies of theprior art.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention provides a phase change memory structureand method for forming the same.

In a first embodiment, the method includes a phase change memorystructure and method for forming the same, the method includingproviding a substrate comprising a conductive area; forming a spacerhaving a partially exposed sidewall electrode at an upper portion of thespacer defining a phase change memory element contact area; and, whereinthe spacer bottom portion partially overlaps the conductive area.

These and other embodiments, aspects and features of the invention willbe better understood from a detailed description of the preferredembodiments of the invention, which are further described below inconjunction with the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F are cross sectional view of a portion of a phase changememory cell at manufacturing stages according to an embodiment of thepresent invention.

FIGS. 2A and 2B are cross sectional views of a portion of a phase changememory cell according to embodiments of the present invention.

FIG. 3 is a process flow diagram including several embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the phase change memory structure and method of forming thesame is explained with reference to an exemplary memory cell, it will beappreciated that the spacer electrode and spacer memory elements formedaccording to embodiments of the invention may be used in the formationof other memory cell structures where a spacer is formed with exposedsidewall electrode at an upper portion to form a contact area of phasechange memory element.

Referring to FIG. 1A, in one embodiment of the present invention a firstinter-layer dielectric (ILD) 12 formed of a conventional silicon oxidedielectric such as PECVD silicon oxide is formed over a substrate (notshown) where the ILD layer includes a conductive area, for example aplug 14A formed by conventional damascene methods. The conductive plugmay be formed of conductive materials such as W, TiN, TiW, TiAl, orTiAlN, or combinations thereof. It will be appreciated that the firstILD layer 12 may be formed of a variety of dielectric insulatingmaterials including PECVD oxide, PETEOS, BPTEOS, BTEOS, PTEOS, TEOS,PEOX, low-K (K<2.9) dielectrics, and fluorine doped silicate glass(e.g., FSG). The conductive plug e.g., 14A provides electricalconnection to a current driving circuit (not shown), for exampleincluding CMOS devices.

Referring to FIG. 1B, a dielectric layer portion 16 (mesa dielectric)formed of a dielectric insulating material such as silicon oxide,preferably PECVD oxide, deposited over the ILD layer 12 andlithographically patterned and etched to form the dielectric portion 16.It will be appreciated that the dielectric layer portion 16 may beformed of one or more of the same preferred insulating dielectrics asoutlined for the first ILD layer. The dielectric portion 16 need not be,but in the present embodiment is shown formed overlapping a portion ofthe conductive plug 14A.

Referring to FIG. 1C, a conductive layer is first blanket deposited byconventional CVD or PVD methods over the process surface followed byetching back the conductive layer by a conventional dry and/or wetetching process to form conductive spacer 18A adjacent the dielectricportion 16 (sidewall) and partially overlapping the conductive plug 14A.Preferably the conductive spacer 18A is formed of a highly conductivematerial readily etchable such as W, TiN, TiW, TiAl, or TiAlN, orcombination thereof. It will be appreciated that the maximum width ofthe spacer 18A may be formed with a variable maximum width dimensionincluding adjusting the amount by which the spacer partially overlapsthe conductive plug 14A, thus adjusting a resistance of the spacer(e.g., electrode).

Referring to FIG. 1D, in an important aspect of the invention, aconventional spin-on-layer (SOL) 20, formed of organic or inorganicmaterial such a spin-on-glass, spin-on dielectric (SOD),benzocyclobutene, or polymides (polyimides), is blanket deposited tocover the spacer 18A, followed by a wet and/or dry etchback processcarried out for a predetermined period of time to uncover (expose) apredetermined portion of the top portion of spacer 18A, e.g., A, theexposed portion forming an electrode contact area (phase changing memoryelement electrode contact area) to a subsequently formed overlying upperelectrode. For example, since the outer portion spacer is 18A is formedwith an exposed sidewall electrode, etchback of the SOL may be carriedfor a predetermined time period to uncover a selected amount of thespacer 18A top portion, e.g., A, thus forming an adjustable electrodecontact area. Thus, the phase changing memory element electrode contactarea (electrode contact area) e.g., A, may be determined by the etchingback process, for example an etching back time period. The electrodecontacting area to the phase changing memory element is preferably assmall as possible, typically is less than about 10000 nm², morepreferably less than about 1000 nm², even more preferably less thanabout 100 nm².

Referring to FIG. 1E, a temperature sensitive (phase change triggering)phase changing (structure changing) material layer, for example achalcogenide including Ge, Te, and Sb, is blanket deposited by aconventional deposition process followed by a photolithographicpatterning of the phase changing layer and a wet and/or dry etchingprocess to form a phase change memory element portion 22A in contactwith the exposed upper portion (electrode contact area), e.g., A of theconductive spacer 18A bottom electrode. It will be appreciated that thedimensions of the memory element portion 22A may be varied, for exampleshown to be about the same width as the bottom electrode (conductiveplug 14A) but may be formed having larger or smaller dimensions.Preferably, however, the memory element portion is formed at least largeenough to cover the exposed portion of the bottom electrode, e.g., Awhich is determined by the etchback time to uncover a predeterminedportion of the upper portion of the spacer 18A.

Referring to FIG. 1F, a second ILD layer 24A formed of the samepreferred materials as the first ILD layer 12 is deposited andplanarized, to electrically isolate the memory element portion 22A,followed by formation of a third planar ILD layer 24B over the secondILD layer followed by formation of a conductive plug e.g., 26A to forman upper electrode according to similar processes and preferredmaterials outlined for forming the first ILD layer 12 and conductiveplug 14A.

Referring to FIG. 2A is shown an exemplary memory cell formed by thepreviously outline steps. For example conductive plugs 14A and 14B areformed in ILD layer 12, spacers 18A and 18B forming bottom electrodes,and an exposed bottom electrode contact area e.g., A, exposed forcontacting a phase change memory elements e.g., 22A and 22B determinedby etchback of SOL layer 20. Dielectric portion 16 is shown formedoverlapping a portion of conductive plugs 14A and 14B allowing formationof thinner spacer bottom electrodes 18A and 18B. Phase change memoryelements 22A and 22B are formed to encompass the electrode contact arease.g., A to form a memory element contact areas over respective spacerbottom electrodes 18A and 18B. Second and third ILD layers 24A and 24Bincluding conductive upper electrode portions 26A and 26B are thenformed as previously outlined.

Referring to FIG. 2B, in another embodiment a similar series of processsteps as outlined for FIGS. 1A through 1F are carried out to form amemory cell except that spacers 28A and 28B now form the phase changingmaterial memory elements where an etchback process of SOL layer 20exposes a portion e.g., B of the upper portion of the spacers to form amemory element electrode contact area with the top electrode. In thisembodiment, the dielectric portion 16 is not formed to partially overlapthe conductive plugs 14A and 142B, which now form the bottom electrodes.In this embodiment the bottom electrode contact area may be adjusted bydetermining the overlap width, W1, the spacers 28A and 28B overlap theconductive plugs 14A and 14B.

Still referring to FIG. 2B, upper electrode portions 30A and 30B arepreferably formed of the same preferred conductive materials as theconductive plugs 14A and 14B, and may be formed of the same or differentpreferred materials. For example, a deposition, lithographic and wet ordry etchback process is carried out to form the upper electrodes 30A and30B. In this embodiment, only a second ILD layer 24A is required toelectrically isolate the upper electrodes 30A and 30B. Similar to thefirst embodiment the memory element electrode contact area (active area)is formed having an area less than about 10000 nm², more preferably lessthan about 1000 nm², even more preferably less than about 100 nm².

Thus, a phase change memory structure and method for forming the same toselectively form an active area to reduce a required drive current hasbeen presented. Advantageously, spacer elements having an exposedsidewall in an upper portion may be formed and an etchback process maybe carried out to uncover a selected portion of the upper portion of thespacer element to form a memory element electrode contact area (activearea). In one embodiment the spacer elements 28A and 28B are formed of aphase change material overlapping on the bottom electrode 14A and 14B.In another embodiment, the spacer elements are formed of a phasechanging material where the uncovered upper portion forms an upperelectrode contact area. Advantageously, the process steps may be carriedout easily and cost effectively, being compatible with existing CMOSformation processes. Advantageously, the memory element electrodecontact area (active area), producing a programmable memory volume ofthe phase change memory element, may be adjustably formed, for example,reduced to decrease a programmable drive current thereby lowering powerconsumption.

Referring to FIG. 3 is a process flow diagram including severalembodiments of the present invention. In process 301, an ILD layerincluding a conductive plug is provided. In process 303, a mesa topdielectric portion is formed over the ILD layer. In process 305, spacerelements forming one of a memory element and memory electrode are formedadjacent the mesa top dielectric portion to overlap a portion of theconductive plug. In process 307, the spacer are covered by an SOL layeran upper portion uncovered to form a phase change memory element contactarea. In process 309, the memory cell is completed including formingeither a memory element over a respective bottom electrode spacer or anupper electrode over a respective spacer memory element.

The preferred embodiments, aspects, and features of the invention havingbeen described, it will be apparent to those skilled in the art thatnumerous variations, modifications, and substitutions may be madewithout departing from the spirit of the invention as disclosed andfurther claimed below.

What is claimed is:
 1. A method for forming a phase change memorystructure comprising: providing a substrate comprising a conductivearea; forming a spacer having a partially exposed sidewall region at anupper portion of the spacer defining a phase change memory elementcontact area; said spacer forming step further comprises forming aspin-on-layer (SOL) over the spacer; and, removing a portion of the SOLto uncover an upper portion of the spacer to define an electrode contactarea for a phase changing memory element; and wherein the spacer bottomportion partially, overlaps the conductive area.
 2. The method of claim1, wherein the spacer comprises a phase changing material sensitive totemperature.
 3. The method of claim 2, wherein the phase changingmaterial comprises a chalcogenide.
 4. The method of claim 3, wherein thechalcogenide comprises a material selected from the group consisting ofGe, Te, and Sb and their alloy system.
 5. The method of claim 2, furthercomprising the step of forming an upper conductive electrode on theelectrode contact area.
 6. The method of claim 5, wherein the upperconductive electrode comprises a material selected from the groupconsisting of W, TiN, TiW, TiAl, TiAlN, and combinations thereof.
 7. Themethod of claim 1, wherein the spacer comprises a conductive material.8. The method of claim 7, wherein the conductive material comprises amaterial selected from the group consisting of W, TiN, TiW, TiAl, TiAlN,and combinations thereof.
 9. The method of claim 7, further comprisingthe steps of: forming a phase changing memory element on the electrodecontact area; and, forming an upper conductive electrode on the phasechanging memory element.
 10. The method of claim 9, wherein the phasechanging memory element comprises a chalcogenide.
 11. The method ofclaim 10, wherein the chalcogenide comprises a material selected fromthe group consisting of Ge, Te, and Sb.
 12. The method of claim 9,wherein the upper conductive electrode comprises a material selectedfrom the group consisting of W, TiN, TiW, TiAl, TiAlN, and combinationsthereof.
 13. The method of claim 1, wherein the spacer is formedadjacent a sidewall of a dielectric insulating portion.
 14. The methodof claim 13, wherein the dielectric insulating portion is formedpartially overlapping the conductive area.
 15. The method of claim 13,wherein the dielectric insulating portion is formed spaced apart fromthe conductive area.
 16. The method of claim 13, wherein the dielectricinsulating portion comprises silicon oxide selected from the groupconsisting of PECVD oxide, PETEOS, BPTEOS, BTEOS, PTEOS, TEOS, PEOX,low-K dielectric, and fluorine doped silicate glass (FSG).
 17. Themethod of claim 1, wherein the SOL layer is selected from the groupconsisting of organic and inorganic materials.
 18. The method of claim17, wherein the SOL layer is selected from the group consisting ofspin-on-glass, benzocyclobutene (BCB), and polyimides.
 19. The method ofclaim 1, wherein the step of removing comprises an etchback processselected from the group consisting of a wet etching and a dry etchingprocess.
 20. A method for forming a phase change memory structurecomprising: providing a substrate comprising a conductive area; forminga spacer having a positive radius of curvature at an upper portion ofthe spacer and the spacer bottom portion partially overlapping theconductive area, the spacer comprising a material selected from thegroup consisting of a temperature sensitive phase changing material anda conductive material; forming a spin-on-layer (SOL) over the spacer;and, removing a portion of the SOL to uncover an upper portion of thespacer to define an electrode contact area for a phase changing memoryelement.